In general the invention pertains to systems for orienting one aircraft with respect to another while in-flight a mechanical link-up between the aircraft such as for aerial refueling operations or the like, and more particularly to a guidance light display suitable for being mounted on the exterior of one of the aircraft for guiding the pilot of the other aircraft into the desired link-up position.
In certain aerial refueling operations, the tanker aircraft is piloted in a level flight path and the receiver aircraft is guided into a link-up position with a refueling boom that extends downwardly and rearwardly from the aft belly section of the tanker aircraft. The boom is swivelably mounted to the tanker aircraft and is telescopically extendable so as to accommodate relative movement between the two aircraft, so long as the receiver aircraft, and more particularly the fuel receptacle thereon, remains within a predetermined refueling evelope centered about an optimum link-up point located at a predetermined distance below the tail of the tanker aircraft. If the receiver pilot is unable to maintain his aircraft within the refueling envelope, then sensors associated with the boom on the tanker aircraft detect that the boom is over or under extended, or has drifted too far to the right or left, or up or down, and automatically causes a decoupling of the boom from the receiver aircraft.
It is evident that the receiver pilot has a difficult task in not only flying his aircraft into the limited region defined by the refueling envelope, but also in maintaining the refueling receptable on his aircraft within the evelope throughout the refueling operation. If, because of a piloting error, or because of adverse air conditions, the automatic decoupling feature causes the boom to become disconnected from the receiver aircraft, then it is necessary for the receiver pilot to repeat the tedious task of recapturing the boom.
Because of the noted difficulty of the operation, guidance systems have been previously proposed for assisting the receiver pilot in the necessary maneuvering of his aircraft. For example, one currently used guidance system provides a guidance-light display mounted on the belly of the tanker aircraft and within the field of view of the receiver pilot in which the lights in the display are selectively operated to direct the receiver pilot to move fore or aft, and up or down, relative to the tanker aircraft. While the guidance afforded by this currently used light display is helpful, it is not totally effective in assisting the pilot under certain operating conditions. For one, the guidance lights are primarily used only after a link-up has been effected, and after link-up the lights are automatically responsive to the various movements of the boom as it conforms to the relative positions of the tanker and receiver aircraft. For example, over-extension of the telescopic boom will automatically cause the guidance-lights to direct the receiver pilot to speed up and thus move forward relative to the tanker aircraft.
While the guidance-lights can also be used prior to link-up for guiding the receiver pilot into the refueling envelope, the lights in such case must be operated manually by a boom operator stationed in the tail section of the tanker aircraft and the manipulation of the lights in this case is subject to observational misjudgements as to the position of the receiver aircraft and slowness in responding to abrupt changes in position. Furthermore, even when the guidance-lights are automatically operated in response to the boom position, after link-up, the guidance-light information is limited to fore-aft position and up-down position. The receiver pilot is responsible for determining his right-left position (azimuth plane) based on his ability to see the outline of the fuselage and tail section of the tanker aircraft. Moreover, no display is provided of the relative velocity between the receiver and the tanker such that it is difficult for the receiver pilot to perceive how fast he is closing on or falling behind the refueling envelope.
These limitations become even more acute when the refueling operation must be performed at night or under limited visbility conditions. In such case, the receiver pilot does not have the benefit of being able to observe the outline of the tanker aircraft, and must rely solely on the effectiveness of the guidance-light display. Because of the limitations of the existing display, refueling during the night, or during other low-visibility conditions, is extremely difficult and hazardous. For tactical reasons, night refueling is sometimes mandatory in order to carry out the refueling operation without enemy observation and thus without consequent enemy interception. For these reasons it would be desirable to provide a guidance-light display system that provided sufficient pilot guidance information for making the refueling operation less hazardous under these special circumstances.
Even when visibility is near perfect, the receiver aircraft pilot has a difficult task in maintaining the receiver receptacle within the refueling envelope for the duration of the refueling operation. It is not unusual to incur one or more automatic disconnects during any refueling operation merely because of the inability of the receiver pilot to maintain the intense concentration and quick response needed to track the tanker aircraft and stay within the refueling envelope. Turbulence and other adverse air conditions can cause rapid shifting of the relative positions of the two aircraft and unless the receiver pilot is capable of correcting for such relative movement, the receiver receptacle may drift outside of the refueling envelope and thereby cause automatic decoupling between the boom and receptacle. To complete the refueling operation, it is necessary for the receiver pilot to repeat the approach sequence necessary for entering the envelope and recapturing the boom. As a result, excessive delays may be incurred in completing the refueling and the receiver pilot may be subjected to undue stress by being forced to repeat the delicate and risky link-up procedure.
In other proposed systems for guiding a receiver pilot into refueling position, instrumentation is mounted within the cockpit of the receiver aircraft for displaying such information as fore-aft, up-down and right-left position in response to optical or radiation sensing equipment that automatically monitors the relative positions of the two aircraft. The displayed information may be in the form of meter readings, or position-indicating blips or dots on the face of a cathode ray tube. While systems of this type provide a greater amount of pilot guidance information, the manner in which it is displayed is less than optimum for the unique conditions of aerial refueling operations. In particular, any meter or cathode ray tube display within the receiver pilot's cockpit, requires the pilot to look back and forth between the tanker aircraft and the instrumentation panel within the cockpit. When the pilot momentarily looks away from the tanker aircraft, to get a fix on the cockpit instrumentation, he increases the risk of accidentally overrunning and colliding with the tanker aircraft or with the refueling boom carried thereby. Furthermore, there is a greater cost involved in equipping all the receiver aircraft in a fleet with refueling guidance systems, as compared to equipping a single tanker that serves the entire fleet.
Accordingly, it is an object of the invention to provide a guidance-light disply of the type suitable for being mounted on the exterior of a lead aircraft for guiding the pilot of a trailing aircraft into position for mechanically linking up the two aircraft, such as for aerial refueling operations, wherein the guidance-light display operates automatically during the pre-link-up approach of the trailing aircraft and continues to operate after link-up to maintain the trailing aircraft at or close to the optimum link-up position.
Another object is to provide such a guidance-light display which informs the pilot in the trailing aircraft as to his position relative to the lead aircraft in three orthogonal axes, fore-aft, elevation and azimuth.
Another object of the invention is to provide such a guidance-light display which in addition to displaying fore-aft, elevational and azimuthal position information, also displays the rate of relative movement in the fore-aft direction so as to indicate to the trailing pilot the rate at which he is closing on, or falling behind the lead aircraft.
A further object of the invention is to provide such a guidance-light display which presents sufficient pilot guidance information so as to enable the pilot of the trailing aircraft to fly into a predetermined link-up position with respect to the lead aircraft under adverse visibility conditions including darkness.
Also it is an object to provide a guidance-light display which is capable of automatic operation in response to position-sensing equipment that automatically senses and calculates the relative position between the lead and trailing aircraft, and does so not only after link-up of the aircraft, but also prior to link-up when the trailing aircraft is approaching the desired link-up position.
Additionally, it is an object to provide a guidance-light display which presents elevational, azimuthal and fore-aft position information along with fore-aft rate information in a format that is capable of being quickly and easily assimulated by the pilot of the trailing aircraft so as to enable him to make timely and accurate flight corrections to attain and thereafter maintain the desired link-up orientation between the aircraft. A related object is to provide a more effective guidance-light display, to enable the pilot to stay within predetermined distances from the optimum link-up position and thereby decrease the likelihood of premature disconnects, which occur automatically when the trailing aircraft moves too far from the optimum link-up position.